1. Field of the Invention
This invention relates generally to techniques for maintaining the position of read/write heads in alignment with tracks of data stored in magnetic media, such as magnetic tape cartridges.
2. Description of the Prior Art
There are many known techniques for maintaining alignment between read/write heads and data tracks stored in magnetic media. One well known conventional technique is commonly called the "buried servo" approach in which data in an underlying magnetic layer having a higher coercivity coating is detected by the read/write head to determine its position with respect to the data track. The servo data in the underlying or buried servo layer typically includes low density, long wavelength data in the form of flux transitions which are not overwritten during the recording or retrieval of data in the upper or information data layer. The timing and the detection of the servo data flux transitions relative to some known reference provides sufficient position information to permit head position corrections to be made by minimizing timing and/or phase errors. Selective filtering is used to discern the servo data in the underlying buried servo track layer from the upper layer read data.
Another well known technique is called the burst or embedded servo approach in which bursts of fixed density flux transitions are located in dedicated or unused gaps which overlap the track centerline to create a pair of distinguishable signals, called the A and B signals, above and below the track centerline, respectively. When the read head tracks the centerline exactly, the A and B signals have equal magnitude. If the head is off-track, the polarity and magnitude of the difference between the A and B signals provides an error signal which can be used to reposition the head.
What is needed is a head positioning technique that doesn't require the use of valuable surface area for servo data, that easily separates servo from information data, and that provides the necessary signals with the required quality to the servo circuitry for accurate head positioning.